In the Third Generation Partnership Project (3GPP) and in the 3GPP Long-Term Evolution (LTE) system, there exists a PDCP layer in the air interface protocol stack of User Equipment (UE) and evolved NodeB (eNB). Due to re-establishment at lower layers, some PDCP packets can be lost, so on those bearers which are mapped to RLC AM, the data-receiving PDCP entity sends PDCP Control PDU or PDCP status report so the peer PDCP entity can re-transmit those missing packets towards the receiver.
Thus, 3GPP LTE Packet Data Convergence Protocol (PDCP) Status Reports are exchanged between UE and eNB. The PDCP specification 3GPP TS 36.323 at the time of the current invention discusses PDCP Status Reports in Section 5.3.
Regarding the transmit operation, section 5.3.1 states that when upper layers request a PDCP re-establishment, for radio bearers that are mapped on RLC AM, the UE shall, if the radio bearer is configured by upper layers to send a PDCP status report in the uplink (statusReportRequired), then compile a status report after processing the PDCP Data PDUs that are received from lower layers due to the re-establishment of the lower layers as specified in subclause 5.2.2.1 and submit it to lower layers as the first PDCP PDU for the transmission, by
(1) setting the FMS field to the PDCP SN of the first missing PDCP SDU;
(2) if there is at least one out-of-sequence PDCP SDU stored, then allocating a Bitmap field of length in bits equal to the number of PDCP SNs from and not including the first missing PDCP SDU up to and including the last out-of-sequence PDCP SDUs, rounded up to the next multiple of 8;
(3) setting as ‘0’ in the corresponding position in the bitmap field for all PDCP SDUs that have not been received as indicated by lower layers, and optionally PDCP SDUs for which decompression have failed;
(4) indicating in the bitmap field as ‘1’ for all other PDCP SDUs.
Regarding the receive operation, section 5.3.2 states that when a PDCP status report is received in the downlink, for radio bearers that are mapped on RLC AM for each PDCP SDU, if any, with the bit in the bitmap set to ‘1’, or with the associated COUNT value less than the COUNT value of the PDCP SDU identified by the FMS field, the successful delivery of the corresponding PDCP SDU is confirmed and the UE shall then process the PDCP SDU as specified in subclause 5.4.
PDCP Control PDU for PDCP status report is discussed in section 6.2.6. Also of interest are RLC status PDU in 36.322, contributions on PDCP Status report for Rel-8, e.g., R2-073225 (Ericsson, “User Plane Status Reports in LTE”, TSG-RAN WG2 Meeting #59, Athens, Greece, Aug. 20-24, 2007) and R2-074124 (LG Electronics Inc., “PDCP Status Report Format”, 3GPP TSG-RAN WG2#59 bis, Shanghai, China, 8 Oct.-12 Oct. 2007).
Extension of PDCP SN, for instance, to 23 bits would mean that problems could develop due to this larger bit size.
This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section. Abbreviations that may be found in the specification and/or the drawing figures are defined below, after the detailed description section.